What's been less closely watched is this story's surprisingly happy ending--or at least its new beginning--some 13 months later. By 5 am on Sept. 18, cars and trucks had been lined up for hours on either side of the Mississippi River. When the St. Anthony Falls Bridge, with its next-gen design, officially opened this month, "it was a solid wall of traffic in both directions for over 8 minutes," says Linda Figg, president of FIGG Engineering Group, which designed the structure based on smarter plans for modern engineering. "We heard stories of people trying to line up at midnight, to be part of the first car entourage to cross the new bridge."

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The story behind the story of this 10-lane, 504-ft bridge is one of the most impressive infrastructure projects of the decade--the complete replacement of a major bridge in little more than a year, months before a deadline that was considered incredibly ambitious. When the team of FIGG Engineering, Flatiron Constructors and Manson Construction won the bid for the project, the date for reopening was set for December 24th of this year. During a visit to the construction site in February, we at Popular Mechanics asked everyone we came across, from taxi drivers to sandwich-shop waiters, whether it seemed like a realistic goal. No one was buying it. Minneapolis winters are too cold for construction, we were told. And why should anyone have faith in U.S. infrastructure when the I-35W had been deemed structurally deficient for years--one of more than 100,000 such bridges scheduled for major overhauls or complete reconstruction?

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But FIGG, Flatiron and Mason pulled off the improbable, and delivered a new bridge in what appears to be an unprecedented time frame. Along the way, the company drew wide praise from infrastructure experts and fellow designers and contractors, employing as much innovation in its construction techniques as in its project management. Construction began well before the final design was completed, with teams of contractors working 12-hour shifts in brutal subzero temperatures. Three of those teams would drill shafts at the same time, instead of one. When conditions on the ground necessitated a shift in the overall bridge design, FIGG made the adjustments on the fly. By shaving off more than three months from the Christmas Eve deadline, FIGG, Flatiron and Mason have earned themselves a hefty bonus.

Their contract with the Minnesota Department of Transportation stipulated an extra $7 million if the bridge opened on time. An earlier opening would mean another $2 million for every ten days before December 24th, with a maximum of $20 million (plus the on-time award of $7 million) if cars were rolling across the St. Anthony Falls Bridge on September 15th. The deal was a doubled-edged sword: If the bridge opened late, the team would lose $200,000 per day. At press time, the Minnesota Department of Transportation had yet to announce the final bonus, but it seems likely that the team will receive either $25 million, or, provided there's enough good will to forgive a few short days, the full $27 million. However that decision shakes out, the larger world of infrastructure is enjoying a rare piece of good news, and a structure that represents the best the industry has to offer. From the history-making pace of construction to the sensors embedded deep in its frame, here's what the St. Anthony Falls Bridge can teach us about building the next generation of American bridges.

Light-Activated, Pollution-Devouring Concrete

As they approach the new bridge, drivers will come across a set of curved 30-ft-long concrete strips just as the bridge begins to span the Mississippi River. The strips a visual reference to the water the bridge is suspended over. But functionally, they're something more groundbreaking. The concrete is mixed with an Italian compound called TX Active, which is designed to turn pollutants--such as sulfur dioxides and carbon monoxide--into salt. This photocatalytic process occurs on the surface of the concrete, and is activated by ultraviolet light. The company that developed TX Active believes that widespread use of the titanium-dioxide-laced compound in urban environments could cut airborne pollution by as much as half, though the limited application in the St. Anthony Falls Bridge isn't likely to have much of an impact on the surrounding environment. They will stand out, though--the smog-eating material is self-cleaning, and should gleam on even the grimiest, slushiest midwinter Minneapolis morning. This is the first major installation of the compound in the United States, and Figg hopes that this primarily aesthetic element will lead to greater recognition of what could be a revolutionary standard in building materials.

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LED Lighting

Although the primary goal of the St. Anthony Falls project was to open a bridge quickly--the Mn-DOT estimated that 140,000 vehicles crossed the old bridge daily, and that detours were costing some $400,000 in revenue per day--Figg wanted to use the new structure as a showcase for smart technology. So the bridge is lit entirely with light-emitting diodes (LED), making it the first application of LED solid-state lighting on a major highway. It's also the longest continuous LED unit, stretching 1300 ft (including the 504-ft span as well as the adjacent roadways on either side) and covering ten lanes of traffic. The LEDs use a fraction of the energy of standard highway lighting, and require significantly less maintenance. "The fixtures themselves last somewhere in the neighborhood of 15 years," says Figg. "Less maintenance means lower energy costs, too. It all adds up."

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Nothing about the St. Anthony Falls Bridge made it a particularly good candidate for LEDs. Which is exactly the point--durable, energy-efficient LEDs should be lining every highway in the country, and as soon as possible.

Self-Consolidating Concrete

The new bridge isn't the first to use self-consolidating concrete, but at least some of the credit for the early-completion bonus goes to the use of this particular concrete mixture. It would have taken significantly longer to painstakingly shovel standard concrete into the 100-ft-deep drill shafts or drop it in and then try to vibrate the mixture into an even distribution. Instead, the team asked a local concrete supplier to create a batch that would be fluid enough for easy pouring, but strong enough to meet the load requirements of a major highway. The goal was for the concrete to be able to bear at least 5000 psi--the final mixture tested at closer to 10,000 psi. That doesn't mean self-consolidating mixtures will become a universal standard because of the need for tighter seams (the more fluid the concrete when it's poured, the more likely it will leak through seams before curing into place). But when time is short, the combination of strength and fluidity will be hard to turn down. "It means less overall labor, less shoveling," Figg says. "It's something that will definitely be used more and more, and probably with great success."

Embedded Sensors

The 323 sensors embedded in different sections of the St. Anthony Falls Bridge are not, for the most part, an early warning system for future collapses. The inherent design of the new bridge, says Figg, makes it much more secure than the previous one. The high-performance, high-strength concrete is more durable. And most important, the bridge is not fracture-critical--meaning that, if one part were to fail, the larger structure would not immediately crumble. There would be time to get drivers off the span, and time to assess the damage.

If such a failure were to occur, some of the sensors, such as the ones that track minuscule amounts of movement throughout the structure, would simply confirm the obvious. Aside from the temperature sensors that automatically trigger the release of anti-icing chemicals, most of the bridge's sensors are intended to improve the business of bridge design and construction. The University of Minnesota, whose campus is practically adjacent to the bridge, will collect and analyze sensor data, "To correlate theoretical design with actual, in-place design," Figg says.

The researchers will track the performance of different materials and construction techniques, and send regular reports to the transportation department. If the system works, the St. Anthony Falls Bridge will serve not only as a symbol of successful infrastructure, but as a source of data for future generations of designers and engineers.

Community Involvement

With millions in bonus dollars on the line, the fact that Figg, Flatiron and Manson asked the Minneapolis community to contribute to the design of the new bridge was unexpected. Even more surprising, though, is that they actually listened. Within two weeks of getting initial approval for the project, the St. Anthony Falls team held a community meeting to discuss specific design elements. A design committee made up of residents from the community and elected and appointed officials voted on many of the bridge's design elements, including the open railings and the transition from the bridge itself to the attached roadways. But in keeping with the overall strategy of nimble, concurrent development, while these and other details were being hammered out, construction on the foundations of the structure had already begun.

The result is a new kind of infrastructure culture, where new ideas are folded into the larger work-in-progress, and no one is waiting for one element to be finished before drawing up plans for the next. And the final product is something that wasn't agreed to in a backroom, or paid for, sight unseen, by a community already rattled by recent tragedy. It was an effort that incorporated decisions from the people who will be driving across it on a daily basis.

Even now, with the bridge fully open to traffic, it remains part of the community it serves: FIGG Engineering is selling scale-model kits of the bridge and a book, The New I-35W Bridge, and donating the proceeds to the Admission Possible program, which helps students from local low-income families to get access to college. If enough money is raised, Figg hopes to create scholarships for Admission Possible students who are pursuing careers in construction or engineering. If there's a way out of the current infrastructure crisis, this project, and all of its ambitions and innovations, is as good a road map as any.